( Reaffirmed 2005 ) IS : 4891- 1988 Indian Standard SPECIFICATION FORPREFERRED CUTSIZESOFSTRUCTURALTIMBER (First Revision ) UDC 674-4 : 691.11 : 389.171 @ Co/ytight 1989 BUREAU MANAK OF BHAVAN, INDIAN ST'ANDARDS ZAFAR MARG 9 BAHADUR SHAH NEW DELHI 110002 Gr2 April 1989 iS:4891-1988 Indian Standard SPECIFICATION FOR PREFERRED CUT SIZES OF STRUCTURAL TIMBER ( First Revision ) 0. 0.1 This Indian FOREWORD 0.2.2 This standard was first published in 1968 and present revision has been undertaken to incorporate the sizes based on experience gained in design and use of timber structural parts as well as from Indian Standards published on the subject. This revision, therefore, contains updated data on sizes adopted in standard designs, door/ window components and deviations in sectional dimensions during conversion for effective shrinkage due to the effect of change in moisture content. 0.2.3 This standard is necessary adjunct to IS : 1331-1971* on cut sizes of timber which cover sizes for all uses. 0.3 For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS : 2-196Ot. The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard. *Specification for cut sizes of timber ( second scuision ). fRules for rounding off numerical values ( rruised). Standard ( First Revision ) was adopted by the Bureau of Indian Standards on 19 September 1988, after the draft finalized by the Building Construction Practices Sectional Committee had been approved by the Civil Engineering Division Council. 0.2 Timber finds its use in several items of construction works, particularly in roof trusses, purlins, rafters, doors, windows, partitions, etc. Due to extreme shortage of timber, there is need for its rational use and this is an essential aspect of timber design. 0.2.1, As a step in this direction, Forest ReseDehra Dun has developed stock arch Institute, designs for a number of standard roof trusses and purlins making it feasible to use the small dimensioned stocks of timber. Based thereon is a need for formulating a set of cut sizes for structural timber. Such a set of preferred cut sizes will facilitate large scale procurement, seasoning, chemical treatment, marketing and prefabrication of various building components as also the dimensional coordination between door frames, partitions, etc. 1. SCOPE 1.1 This standard covers preferred timber for use in the following units: a) Roof trusses; b) Roof purlins, rafters, floor beams, etc; cut sizes of with IS : 1141-1973* and IS : 401-1982t. 2.2 For centering the preferred sizes shall be the same as for partition framing covered in Table 3. 2.3 Tolerances 2.3.1 a) 1) For measurement 2) Measurement up to 100 mm: Oto+3mm above 100 mm: -3 to +6 mm c) Partitions d) Centering; framing, and covering; e) Door/window/ventilators. 2. PREFERRED SIZES b) Length for all sizes: Oto+lOmm 2.1 Preferred cut sizes shall be as covered in Tables 1 to 4. These sizes are sawn sizes obtained from air dried timbers. The seasoning and preservation of timber is carried out in accordance *Code of practice for seasoning of timber. *Code of practice for preservation of timber ( third reuision) . 1 '33:48!u-1988 TABLE 1 PREFERRED CUT SIZES OF STRUCTURAL TIMBERS ( SPAN FROM 3 TO 20 METRES ) ( clause 2.1 ) THICKNESS IN mm 20 25 30 35 40 50 60 80 NOTE 1 NOTE 2 WIDTH IN mm 60 60 60 60 60 60 80 80 8b 80 80 80 80 100 100 100 100 100 100 100 100 FOR ROOF TRUSSES ~______--~----*---40 50 40 40 50 50 -- --------~ 120 120 120 120 120 120 120 140 140 140 140 140 140 140 160 160 160 160 160 160 160 For truss spasmsmarginally Preferred lenghts of timber above 20 m, preferred cut sizes of structural timber may be allowed. : I, 1'5, 2,2'5 and 3 m. TABLE 2 PREFERRED CUT SIZES OF STRUCTURAL RAFTERS, FLOOR BEAMS, i Clause 2.1 ) TIMBER ETC FOR ROOF PURLINS, THICKNESS IN mm 50 60 80 100 NOTE Preferred c---_--_--_---80 100 80 lengths of timber: 100 100 - 120 120 120 - WIDTH IN mm A--_-----_-_--__-_--__ 140 140 140 140 160 160 160 180 200 1'5, 2, 2.5 and 3 m. TABLE 3 PREFERRED CUT SIZES OF STRUCTURAL TIMBERS FRAMING AND COVERING ( Clauses 2.1 and 2.2 ) FOR PARTITION THICKNESS IN mm 10 15 20 25 30 40 50 60 80 NOTE : Preferred r____--___---.---40 50 40 40 40 40 40 50 50 50 50 50 - 60 GO 60 60 60 60 60 - 80 80 80 80 80 80 80 80 80 WIDTH IN mm A---_-__--------_---~ _ _ 100 100 100 100 100 100 100 100 120 120 120 120 120 120 120 160 160 160 160 160 160 160 200 200 "00 200 200 200 200 240 240 240 240 240 240 lenghts of timber : O-5, 1, 1.5, 2, 2.5 and 3 m. 2 IS:4891- 1988 TABLE 4 PREFERRED CUT SIZES OF TIMBER FOR DOOR/WINDOW/VENTILATOR COMPONENTS ( Clause 2.1 ) THICICNESS IN mm 15 20 25 30 35 40 50 60 NOTE 1 WIDTH IN mm 60 60 60 60 60 80 80 80 80 80 80 100' 100 100 100 100 100 100 120 120 _ 140 160 160 160 180 _ 200 c 220 _ 240 _240 240 - C___________--_-__---~h-,--_-------------~ ____----25 30 timber 35 _ 40 _ lengths 50 50 50 i~0 50 - Preferred ( wall opening module of 1OC mm ) for frames: 590, 790, 890, 990, 1 190, 1 290, 1 990 and 2 090 mm. Preferred timber lengths for shutters: 460,500,560, 700, 800,900, 1 100, 1 209,l 905 and 2 005 mm. NOTE 2 - For beading width may be allowed. of 15 mm thickness, 25 and 40 mm width, and for 20 mm thickness, 150 and 200 25,30 and 40 mm for 50 mm NOTE 3 - For lock and bottom rail of 30, 35 and 40 mm thickness, 150, 200 and 240 mm width may be allowed. thickness, mm width and 2.3.2 Tolerances in door/window/ventilators components shall be permissible as under: a) b) Frames Shutters 1) Doors i) Width ii) Thickness for panels etc &l mm -&3 mm No tolerance Width Above *3mm fl mm *3 mm the oven-dry weight according to IS : 287-1973*. Thus a lateral shrinkage effect in the stocked sizes of timber will take place and, therefore, the ultimate shrinkage to which the timber will be subjected to has got to be compensated in the very first instance at the time of converting the timber at 20 percent moisture content for stocking purposes. 2.3.4 A method for adjustment of dimensions different moisture content is given in Appendix along with an illustrative example. at A 2) Window/ventilators, 40 mm and less 40 mm 2.3.3 Cut sizes of timber as stocked and specified in tables are normally at moisture content of 20 percent. But at the time of fabrication and erection, the timber members are required to possess 12 to 20 percent of moisture content of 2.3.5 Other sizes may be produced or stocked to meet specific demands or to ensure full utilization of the logs or their off-cuts. *Recommendations for maximum permissible moisture content for timber used for different purposes ( second 7eCsion ) . . APPEN DIX A ( Clause 2.3.4 ) ADJUSTMENT A-l. OF DIMENSIONS taken AT DIFFERENT as MOISTURE CONTENTS All the tabulated sizes shall be standard at 20 percent moisture content.* A-3. For cross-sectional dimensions, the following allowances shall be made irrespective of radial or tangential directions. A-3.1 For timbers of specific gravity below O-6 ( or dimensional stability 60 percent of teak and A-2. For dimensions along the grain, no allowances shall be made for moisture content differing from 20 percent moisture contents. 3 IS : 4891 - 1988 above ), the change in the dimensions shall be calculated on the basis of 0.2 percent per unit moisture content differing from standard 20 percent moisture content. A-3.2 For species of specific gravity 0.6 and above ( or dimensional stability below 60 percent of teak ), the change in the dimensions shall be calculated on the basis of O-3 percent per unit moisture content differing from standard 20 percent moisture content. A-3.3 Example; b) 4 Difference in moisture content between time of storing and the time of use later Now for 1 percent difference in moisture content, percentage deviation in corresponding dimension = 20-12 = 8 percent = 0.2 percent ( for. timber species with specific gravity below 0.6 ) 0.2 x 8 percent l-6 percent 1 6percent of x 0.016xmm 4 e) Data For 8 percent difference in moisture content, percentage deviation For 8 percent difference in moisture content, the physical deviation from corresponding dimension at the time of sawing and storing x 0.016 x will or x have to be = = = = 1) Exact dimension required for actual fabrication later according to the engineering drawing at the later = 100 mm 2) 3) Moisture content time of fabrication = = 12 percent 20 percent f 1 Therefore, = = 100mm 101*63mm Moisture content in the first instance at the time of sawing and storing the gravity of 4) Specific timber species used = below 0.6 S0LlJ770M a) Let the dimension first instance at the sawing/storing be in the time of = x mm Similarly, the corresponding dimensions ( that is, 1.63 mm oversize ) in the first instance at the time of sawing/storing for all the four zones into which India is divided according to moisture content vide IS : 287-1973* can be worked out. *Recommendations far maximllm permissible moisture content for timber used for different purposes ( second revision ) . 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